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+netdata plugins
+===============
+
+Any program that can print a few values to its standard output can become
+a netdata plugin.
+
+There are 5 lines netdata parses. lines starting with:
+
+- `CHART` - create a new chart
+- `DIMENSION` - add a dimension to the chart just created
+- `BEGIN` - initialize data collection for a chart
+- `SET` - set the value of a dimension for the initialized chart
+- `END` - complete data collection for the initialized chart
+
+a single program can produce any number of charts with any number of dimensions
+each.
+
+charts can also be added any time (not just the beginning).
+
+### command line parameters
+
+The plugin should accept just **one** parameter: **the number of seconds it is
+expected to update the values for its charts**. The value passed by netdata
+to the plugin is controlled via its configuration file (so there is not need
+for the plugin to handle this configuration option).
+
+The script can overwrite the update frequency. For example, the server may
+request per second updates, but the script may overwrite this to one update
+every 5 seconds.
+
+### environment variables
+
+There are a few environment variables that are set by `netdata` and are
+available for the plugin to use.
+
+variable|description
+:------:|:----------
+`NETDATA_CONFIG_DIR`|The directory where all netdata related configuration should be stored. If the plugin requires custom configuration, this is the place to save it.
+`NETDATA_PLUGINS_DIR`|The directory where all netdata plugins are stored.
+`NETDATA_WEB_DIR`|The directory where the web files of netdata are saved.
+`NETDATA_CACHE_DIR`|The directory where the cache files of netdata are stored. Use this directory if the plugin requires a place to store data. A new directory should be created for the plugin for this purpose, inside this directory.
+`NETDATA_LOG_DIR`|The directory where the log files are stored. By default the `stderr` output of the plugin will be saved in the `error.log` file of netdata.
+`NETDATA_HOST_PREFIX`|This is used in environments where system directories like `/sys` and `/proc` have to be accessed at a different path.
+`NETDATA_DEBUG_FLAGS`|This is number (probably in hex starting with `0x`), that enables certain netdata debugging features.
+`NETDATA_UPDATE_EVERY`|The minimum number of seconds between chart refreshes. This is like the **internal clock** of netdata (it is user configurable, defaulting to `1`). There is no meaning for a plugin to update its values more frequently than this number of seconds.
+
+
+# the output of the plugin
+
+The plugin should output instructions for netdata to its output (`stdout`).
+
+## CHART
+
+`CHART` defines a new chart.
+
+the template is:
+
+> CHART type.id name title units [family [category [charttype [priority [update_every]]]]]
+
+ where:
+  - `type.id`
+
+    uniquely identifies the chart,
+    this is what will be needed to add values to the chart
+
+  - `name`
+
+    is the name that will be presented to the used for this chart
+
+  - `title`
+
+    the text above the chart
+
+  - `units`
+
+    the label of the vertical axis of the chart,
+    all dimensions added to a chart should have the same units
+    of measurement
+
+  - `family`
+
+    is used to group charts together
+    (for example all eth0 charts should say: eth0),
+    if empty or missing, the `id` part of `type.id` will be used
+
+  - `category`
+
+    the section under which the chart will appear
+    (for example mem.ram should appear in the 'system' section),
+    the special word 'none' means: do not show this chart on the home page,
+    if empty or missing, the `type` part of `type.id` will be used
+
+  - `charttype`
+
+    one of `line`, `area` or `stacked`,
+    if empty or missing, the `line` will be used
+
+  - `priority`
+
+    is the relative priority of the charts as rendered on the web page,
+    lower numbers make the charts appear before the ones with higher numbers,
+    if empty or missing, `1000` will be used
+
+  - `update_every`
+
+    overwrite the update frequency set by the server,
+    if empty or missing, the user configured value will be used
+
+
+## DIMENSION
+
+`DIMENSION` defines a new dimension for the chart
+
+the template is:
+
+> DIMENSION id [name [algorithm [multiplier [divisor [hidden]]]]]
+
+ where:
+
+  - `id`
+
+    the `id` of this dimension (it is a text value, not numeric),
+    this will be needed later to add values to the dimension
+
+  - `name`
+
+    the name of the dimension as it will appear at the legend of the chart,
+    if empty or missing the `id` will be used
+
+  - `algorithm`
+
+    one of:
+
+    * `absolute`
+
+      the value is to drawn as-is (interpolated to second boundary),
+      if `algorithm` is empty, invalid or missing, `absolute` is used
+
+    * `incremental`
+
+      the value increases over time,
+      the difference from the last value is presented in the chart,
+      the server interpolates the value and calculates a per second figure
+
+    * `percentage-of-absolute-row`
+
+      the % of this value compared to the total of all dimensions
+
+    * `percentage-of-incremental-row`
+
+      the % of this value compared to the incremental total of
+      all dimensions
+
+  - `multiplier`
+
+    an integer value to multiply the collected value,
+    if empty or missing, `1` is used
+
+  - `divisor`
+
+    an integer value to divide the collected value,
+    if empty or missing, `1` is used
+
+  - `hidden`
+
+    giving the keyword `hidden` will make this dimension hidden,
+    it will take part in the calculations but will not be presented in the chart
+
+
+## data collection
+
+data collection is defined as a series of `BEGIN` -> `SET` -> `END` lines
+
+> BEGIN type.id [microseconds]
+
+  - `type.id`
+
+    is the unique identification of the chart (as given in `CHART`)
+
+  - `microseconds`
+
+    is the number of microseconds since the last update of the chart,
+    it is optional.
+
+    Under heavy system load, the system may have some latency transfering
+    data from the plugins to netdata via the pipe. This number improves
+    accuracy significantly, since the plugin is able to calculate the
+    duration between its iterations better than netdata.
+
+    The first time the plugin is started, no microseconds should be given
+    to netdata.
+
+> SET id = value
+
+   - `id`
+
+     is the unique identification of the dimension (of the chart just began)
+
+   - `value`
+
+     is the collected value
+
+> END
+
+  END does not take any parameters, it commits the collected values to the chart.
+
+More `SET` lines may appear to update all the dimensions of the chart.
+All of them in one `BEGIN` -> `END` block.
+
+All `SET` lines within a single `BEGIN` -> `END` block have to refer to the
+same chart.
+
+If more charts need to be updated, each chart should have its own
+`BEGIN` -> `SET` -> `END` block.
+
+If, for any reason, a plugin has issued a `BEGIN` but wants to cancel it,
+it can issue a `FLUSH`. The `FLUSH` command will instruct netdata to ignore
+the last `BEGIN` command.
+
+If a plugin does not behave properly (outputs invalid lines, or does not
+follow these guidelines), will be disabled by netdata.
+
+
+### collected values
+
+netdata will collect any **signed** value in the 64bit range:
+`-9.223.372.036.854.775.808` to `+9.223.372.036.854.775.807`
+
+Internally, all calculations are made using 128 bit double precision and are
+stored in 30 bits as floating point.
+
+If a value is not collected, leave it empty, like this:
+
+`SET id = `
+
+or do not output the line at all.